IOS SDK详解之NSDictionary

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原创Blog，转载请注明出处
blog.csdn.net/hello_hwc

前言：本文将要讲述的内容有
1.NSDictionary 以及 NSMutableDictionary 概述
2.常用属性方法举例（不常用的本文不会涉及）

一 NSDictionary/NSMutableDictionary概述
NSDictionary提供了一种key－value的数据存储方式。总的来说，任何对象都可以作为key，只要其遵循NSCopying协议。其中，key不能相同（由isEqual来判断）。key和value都不能为nil，如果要表达一个空的值，用NSNull。NSDictionary中的值不可变。
NSMutableDictionary是NSDictionary的子类，是可变的字典。

二 NSDictionary常用的属性方法举例

2.1 创建和初始化
创建兼初始化

(instancetype)dictionaryWithContentsOfFile:(NSString *)path(instancetype)dictionary;(instancetype)dictionaryWithDictionary:(NSDictionary *)(instancetype)dictionaryWithObjects:(NSArray *)objects   forKeys:(NSArray *)keys(instancetype)dictionaryWithObjectsAndKeys:(id)firstObject

初始化

-(NSDictionary *)init;-(NSDictionary *)initWithContentsOfFile:(NSString *)path;-(NSDictionary *)initWithDictionary:(NSDictionary *);-(NSDictionary *)initWithObjects:(NSArray *)objects   forKeys:(NSArray *)keys;-(NSDictionary *)initWithObjectsAndKeys:(id)firstObject;

就个人而言，我比较习惯后一种。当然，快捷创建的方式不要忘记了
符号

@{}

举例：

    NSDictionary * emptyDic = [NSDictionary dictionary];    NSDictionary * firstDic = @{@"key":@"value",                                @"first":@"1"};    NSDictionary * secondDic = [[NSDictionary alloc] initWithObjectsAndKeys:@"value1",@"key1",@"value2",@"key2",nil];

2.2 count
返回key－value对的个数

    NSDictionary * dic = @{@"key1":@"1",                           @"key2":@"2"};    NSLog(@"%d",dic.count);

2.3 isEqualToDictionary比较两个dictionary内容是否一样。

    NSDictionary * dic1 = @{@"key1":@"1",                           @"key2":@"2"};    NSDictionary * dic2 = @{@"key2":@"2",                            @"key1":@"1"};    if ([dic1 isEqualToDictionary:dic2]) {        NSLog(@"Equal contents");    }

2.4 objectForKey: 和valueForKey 由属性获得内容

    NSDictionary * dic1 = @{@"key1":@"1",                           @"key2":@"2"};    NSLog(@"%@",[dic1 objectForKey:@"key1"]);    NSLog(@"%@",[dic1 valueForKey:@"key2"]);

2.5 allKeys 和 allValues 获得所有的key/value

    NSDictionary * dic1 = @{@"key1":@"1",                           @"key2":@"2"};    NSArray * keys = [dic1 allKeys];    NSArray * values = [dic1 allValues];

2.6 enumerateKeysAndObjectsUsingBlock 用Block的方式遍历

这里的stop决定了是否停止遍历。NSDictionary * dic1 = @{@"key1":@"1",                           @"key2":@"2"};[dic1 enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {        NSLog(@"%@=>%@",[key description],[obj description]);    }];

2.7 排序
keysSortedByValueUsingSelector:
keysSortedByValueUsingComparator :
keysSortedByValueWithOptions: usingComparator:
返回Keys的数组，顺序按照value排序顺序。

  NSDictionary * numsDic = @{@(2):@"second",                               @(1):@"first",                               @(3):@"thrid"};    NSDictionary * strDic = @{@"id_1":@"first",                              @"id_3":@"thrid",                              @"id_2":@"second"};    NSArray * numsSortedKeys = [numsDic keysSortedByValueUsingSelector:@selector(compare:)];    NSArray * strSortedKyes = [strDic keysSortedByValueUsingComparator:^NSComparisonResult(id obj1, id obj2) {        NSString * str1 = obj1;        NSString * str2 = obj2;        return [str1 compare:str2];    }];    NSLog(@"%@",numsSortedKeys.description);    NSLog(@"%@",strSortedKyes.description);

输出

2015-02-09 22:04:12.070 DictonaryExample[1037:23292] (
1,
2,
3
)
2015-02-09 22:04:12.070 DictonaryExample[1037:23292] (
“id_1”,
“id_2”,
“id_3”
)

2.8 过滤
keysOfEntriesPassingTest：
返回keys的集合，这些keys符合参数block的约束

  NSDictionary * numsDic = @{@(2):@"second",                               @(1):@"first",                               @(3):@"thrid"};  NSSet * filteredKyes = [numsDic keysOfEntriesPassingTest:^BOOL(id key, id obj, BOOL *stop) {        BOOL result = NO;        NSNumber * numKey = key;        if (numKey.integerValue > 2) {            result =  YES;        }        return result;    }];    NSLog(@"%@",filteredKyes.description);

输出

2015-02-09 22:09:50.800 DictonaryExample[1099:25241] {(
3
)}

2.9写到文件
writeToFile:atomically
writeToURL:atomically

   NSString * path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject] ;    NSString * fileName = @"file";    NSString * filePath = [path stringByAppendingPathComponent:fileName];    NSDictionary * dic = @{@"key":@"value"};    BOOL result = [dic writeToFile:filePath atomically:YES];    if (result) {        NSLog(@"Success");    }

2.10Description－常常用来debug输出dictionary的内容。
在之前已经举例好多了，这里不再赘述

三 NSMutableDictionary的额外方法
3.1 添加元素

- (void)setObject:(id)anObject           forKey:(id<NSCopying>)aKey- (void)setValue:(id)value          forKey:(NSString *)key- (void)setDictionary:(NSDictionary *)otherDictionary

注意，使用KVC的时候，key一定要是NSString。第三个函数是删除之前的元素，然后把otherDictionary元素放到当前dic中。
举例

    NSMutableDictionary * dic = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@"object",@"key", nil];    NSLog(@"%@",dic.description);    [dic setDictionary:@{@"otherKey":@"otherValue"}];    NSLog(@"%@",dic.description);

输出

2015-02-09 22:31:21.417 DictonaryExample[1232:31666] {
key = object;
}
2015-02-09 22:31:21.418 DictonaryExample[1232:31666] {
otherKey = otherValue;
}

3.2删除元素

- (void)removeObjectForKey:(id)aKey- (void)removeAllObjects- (void)removeObjectsForKeys:(NSArray *)keyArray

比较容易忽视的是第三个，删除一组key。
举例

 NSDictionary * dic = @{@(1):@"first",                           @(2):@"second",                           @(3):@"thrid"};    NSMutableDictionary * mutableDic = [[NSMutableDictionary alloc] initWithDictionary:dic];    [mutableDic removeObjectsForKeys:@[@(1),@(2)]];    NSLog(@"%@",mutableDic.description);

输出

2015-02-09 22:34:13.112 DictonaryExample[1273:32793] {    3 = thrid;}

BTY：年前计划在更新一篇KVC 和 KVO的详细讲解。然后继续更新GCD系列的第五篇。如果精力够用的话，更再更新一篇Swift相关的。

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